microdroid_manager waits for task to exit

If microdroid_manager doesn't do the wait, the child process which might
not have run to completion is force killed by init, because
microdroid_manager is registered as a oneshot service.

Bug: N/A
Test: atest MicrodroidHostTestCases
Change-Id: I5748fbbb233182f0d8ca885bd94c7d15149aae82
1 file changed